An air-water heat pump is a mechanical device that extracts heat from the outside air and uses it to heat water for radiators, underfloor heating, hot taps, showers, and baths. It works by transferring heat from the ambient air to a coolant which is then compressed to increase its temperature to heat the water. The heat pump uses electricity to power the compressor and fan, but this only uses a fraction of the thermal energy that is provided. The refrigerant in the heat pump reverts to liquid form and can be reused in the process. Find out more about different types of heat pumps here.